Which factors determine "size" in selecting the world's largest port? Different factors and assessment criteria produce different answers. Accordingly, the result could be specified as "HMSS," which in this case does not stand for Her Majesty's Steam Ship.

For those to whom the traffic figures of commercial vessels are relevant, the biggest port is the one with the highest traffic numbers. Singapore's Maritime and Port Authority points out that its port is "the world's busiest port in terms of shipping tonnage," with 1.04 billion gross tons and 133,185 calls last year, although the number of calls dropped slightly from 135,386 in 2003.

The criterion is different if the dominant port traffic is cruise liners. With some 3.5 million passengers in 2004, the Port of Miami is confident and correct in claiming to be the Cruise Capital of the World. But with fewer than 10 million tons of cargo last year, Miami ranks further down the scale in that category. This does not in any way minimize Miami's position but is merely intended to encourage a differentiated consideration of the question at stake.

For the majority of ports throughout the world, the transport of cargo is the supporting pillar of the business. Most ports have been built for the international transit of goods, and the obvious criteria - "number and size of vessels" - are used to determine the port's size and importance. But particularly since the 1960s and the introduction of standard containers, the number of TEUs handled has become the relevant indicator, one that can be effortlessly compared internationally. There usually is no differentiation between full containers and the consignment of empties.

With 22.5 million TEUs, Hong Kong headed the list of the world's biggest container ports in 2004, followed by Singapore with 21.3 million and Shanghai with 14.6 million. Hong Kong has been the busiest container port for a number of years. That may change in the future, because the growth rates indicate a reversal of the list of the top three ports. In 2004, the container traffic growth rates were 29 percent for Shanghai, 15.9 percent for Singapore and 8.1 percent for Hong Kong. Nevertheless, for now, in containers, Hong Kong is king.

But ports also handle bulk cargoes - including petroleum, ores, coal or agricultural products - that are not customarily transported in containers. In this context, the weight measured in metric tons has proved a useful indicator.

Because of the long tradition of the shipping industry and various international perceptions of "one ton," caution must be taken to avoid incorrect evaluations. One metric ton corresponds to 1,000 kilograms; however, in the U.S. and Canada, one ton often means a short ton (2,000 pounds, or 907.185 kilograms). In Great Britain, however, the term "long ton" is widely used. A long ton is 1,016.047 kilograms, or 2,240 pounds.

To set the metric ton apart from the short and long ton, it is referred to as "tonne" in Britain, although the English spelling of metric ton with one "n" is correct.

Some, but not all, ports count their cargo volume in metric tons. Even renowned trade journals do not always take this into consideration and may thus arrive at wrong conclusions. One recent report declared Singapore the world's biggest port, with a volume of 388 million tons. Another port magazine listed Shanghai as the biggest port, with 370 million tons handled last year, and said Rotterdam was the previous leader but fell to second with 350 million tons.

The explanation is that Singapore measures its cargo in "freight tons," a combined weight and/or volume-measuring unit that uses either metric tons or volume units (1 foot equals 40 cubic foot or 1.1326 cubic meters) and is generally used by ship operators in calculating freight rates. In accordance with that economic objective, the freight ton is referred to as bill-of-lading ton or revenue ton. A rough conversion indicates that the cargo handled in Singapore in 2004 was approximately 300 million metric tons.

The Port of Rotterdam journal recently entitled an article "Congratulations to Shanghai." For 42 years, Rotterdam was the world's biggest port - measured in metric tons. But in 2004, this title was passed to Shanghai, which, with 370 million metric tons, is undisputedly the biggest port in the handling of goods.

Which port is biggest? Depending on the measurement, the answer could be Hong Kong, Miami, Singapore or, last but not least, Shanghai. If we string together the first letters of each of these ports, then the biggest ports are: HMSS, or Hong-Mi-Sing-Sha.

Juergen Sorgenfrei is chairman of HMM (Port of Hamburg Marketing) at of Hamburg, which is Germany's largest port and - depending on how you measure it - one of the world's largest. He can be contacted at sorgenfrei@hafen-hamburg.de.